Functional assessment of the cell-autonomous role of NADase CD38 in regulating CD8⁺ T cell exhaustion

Exhausted CD8⁺ T cells with limited effector functions and high expression of multiple co-inhibitory receptors are one of the main barriers hindering antitumor immunity. The NADase CD38 has received considerable attention as a biomarker of CD8⁺ T cell exhaustion, but it remains unclear whether the increased CD38 directly promotes T cell dysfunctionality. Here, we surprisingly found that although Cd38 deficiency partially reverses NAD⁺ degradation and T cell dysfunction in vitro, the terminal exhausted differentiation of adoptively transferred CD8⁺ T cells in tumor is not impacted by either deficiency or overexpression of CD38. Monitoring the dynamic NAD⁺ levels shows that NAD⁺ levels are comparable between tumor infiltrated WT and Cd38^−/− OT-1 cells. Therefore, our results suggest that decreased NAD⁺ are correlated with T cell dysfunction, but deficiency of CD38 is not enough for rescuing NAD⁺ in tumor infiltrated CD8⁺ T cells and fails to increase the efficacy of antitumor T cell therapy.